1. Field of the Invention
Example embodiments of the present invention relate generally to semiconductor devices, a system including semiconductor devices and methods thereof, and more particularly to semiconductor devices, a system including semiconductor devices and methods of reducing noise.
2. Description of the Related Art
Noise may occur due to parasitic inductance in a parallel input/output circuit of a semiconductor device (e.g., a dynamic random access memory (DRAM) device or a controller) using single-ended parallel transmission for a single-ended interface.
FIG. 1 is a schematic diagram of a conventional single-ended parallel interface system 10. The single-ended parallel interface system 10 may include a first semiconductor device 20 having a transmitter 21 and a plurality of transmission lines Line1 through LineN, and a second semiconductor device 30 having a receiver 31. The transmitter 21 may include a plurality of transmission drivers 101 through 10N. The receiver 31 may include a plurality of amplifiers 201 through 20N and a plurality of terminating resistors R1 through RN.
Referring to FIG. 1, the total amount of current consumed by the transmission drivers 101 through 10N may vary based on values DQ1 through DQN of N bits of parallel data transmitted through the transmission lines Line1 through LineN. Because parasitic inductance may occur between internal power supply nodes VDDQ and VSSQ and respective board power supply nodes VDD and VSS, a change in current flowing due to the parasitic inductance may raise noise (e.g., jitter, voltage noise, or reference fluctuation) in the internal power supply nodes VDDQ and VSSQ. The noise may be proportional to the variation in current flowing in all channels (e.g., the transmission lines Line1 through LineN). Such noise may also reduce the voltage margin and the time margin of a signal, limiting a transmission rate or frequency.
Referring to FIG. 1, in order to reduce noise, differential signaling, in which a substantially constant current is consumed, may be employed. However, differential signaling may require additional pins (e.g., twice as many pins) as compared to single-ended signaling.
Another conventional process for reducing noise may be DC balance coding. FIG. 2 illustrates a conventional single-ended parallel interface system 200 using DC balance coding. The single-ended parallel interface system 200 may include a first semiconductor device 210 and a second semiconductor device 220.
Referring to FIG. 2, the first semiconductor device 210 may include a core block 211, a balance encoding block 212 and an output driver 213. The core block 211 may store given first parallel data. The balance encoding block 212 may receive and encode the first parallel data from the core block 211 and may output second parallel data. The output driver 213 may receive the second parallel data and may output the received second parallel data to the second semiconductor device 220.
Referring to FIG. 2, the second semiconductor device 220 may include a receiver 221, a decoding block 222 and a data storage unit 223. The receiver 221 may receive an output from the output driver 213. The decoding block 222 may decode parallel data output from the receiver 221 to restore the first parallel data. The data storage unit 223 may store the restored first parallel data.
Referring to FIG. 2, the balance encoding block 212 may perform encoding using the DC balance coding. Examples of DC balance coding may be 8B/10B coding and data bus inversion (DBI) coding. In conventional 8B/10B coding, 2 bits of data may be added to 8 bits of parallel data so that a number of bits set to a first logic level (e.g., a higher logic level or logic “1”) may be similar to a number of bits set to a second logic level (e.g., a lower logic level or logic “0”). Thus, conventionally, a maximum difference between the number of bits set to the first and second logic levels may typically be set to be 2 in a DC balance code having 10-bit parallel data such that noise occurring in the internal power supply nodes VDDQ and VSSQ may be reduced to a quarter.
Referring to FIG. 2, in conventional DBI coding, the number of bits set to the first and second logic levels, respectively, may be calculated in N-bit (e.g., 8-bit) parallel data. If the calculated number bits set to the first or second logic level exceeds a threshold value “k” (e.g., where k≧4), the N-bit parallel data may be inverted and a first flag may be set to, for example, the first logic level (e.g., a higher logic level or logic “1”) during coding.
In each of 8B/10B coding and DBI coding, the number of bits set to the first and second logic levels, respectively, in parallel data may be controlled to reduce the variation in current flowing in parasitic inductance between the internal power supply nodes VDDQ and VSSQ and the respective board power supply nodes VDD and VSS, thereby reducing noise. Accordingly, DC noise may be reduced using the conventional DC balance coding.
However, 8B/10B coding and DBI coding may not reduce switching noise occurring if an input bit value in parallel data changes temporally. For example, if a 10-bit balance code is converted from a first code of “0000011111” into a second code of “1111100000”, each respective bit of the first code changes during the conversion, and therefore, noise caused by switching of input data values may increase.